Method for attaching a torque measuring device

ABSTRACT

In a method for fastening a torque measurement device for detecting a relative torque between an input shaft and an output shaft of a steering system, e.g., of a rack-and-pinion power-assisted steering system, the torque measurement device is integrally formed locally into the input shaft and/or the output shaft by deformation elements.

FIELD OF THE INVENTION

The present invention relates to a method for fastening a torquemeasurement device for detecting a relative torque between an inputshaft and an output shaft. The present invention also relates to aninput shaft and/or output shaft for performing the method.

BACKGROUND INFORMATION

In steering systems, in particular in power-assisted steering systems,in which manual steering is assisted by an electric motor, an exact,reliable and permanent detection of a relative torque between an inputshaft and an output shaft is particularly important for ascertaining thesteering requirement. The torque measurement device used for detectionis in this case generally installed between an input shaft, which isconnected to a steering spindle connection, and an output shaft, whichis connected to a pinion. The torque measurement device thus detects therelative torque between the steering spindle connection or input shaftand the pinion or output shaft and controls the drive of an electricmotor via an electronic module. The electric motor may in this caseserve for the power assistance of the conventional steering apparatus.

As regards the operating principle of a rack-and-pinion power-assistedsteering system, reference is made, in this regard, to EuropeanPublished Patent Application No. 0 366 691.

A method, conventional from practice, for fastening a torque measurementdevice to an input shaft and an output shaft of a steering systemprovides, in this context, for the torque measurement device to bewelded to the input shaft and the output shaft. It became clear in thiscase, however, that this welded joint is complicated and notsufficiently reliable. A break of the weld seam may occur, for example,when the wrong material is welded. Since the torque measurement deviceis a safety-relevant element which is to operate with high precision andreliably, the fastening method must satisfy particularly stringentdemands and possibilities of error must be ruled out as far as possible.

It is an aspect of the present invention to overcome disadvantages ofthe prior art, in particular to provide a method of the type initiallymentioned, which allows an accurate, reliable and permanent fastening ofa torque measurement device between an input shaft and an output shaftof a steering system and may be performed in a favorable and simplemanner and which may largely rule out error sources which may lead to arelease of the connection.

SUMMARY

Since the torque measurement device is integrally formed locally intothe input shaft and/or the output shaft by deformation elements, areliable, permanent and exact connection is obtained, which virtuallyrules out an inadvertent release of the torque measurement device, forexample due to the choice of wrong material. Moreover, the method can becarried out simply, quickly and cost-effectively. The connection iscorrosion-proof, vibration-proof, temperature-resistant, resistant tophysical influences, etc.

The connection made by the method according to an example embodiment ofthe present invention may have, moreover, particularly high strength.The torque measurement device may be fastened exactly in the intendedposition.

It may be provided that even materials which may not be welded to oneanother may be connected. A choice of the materials to be processedwhich is determined by welding criteria may therefore be dispensed with.According to an example embodiment of the method, fastening may also beperformed particularly cost-effectively because round parts may beconnected to one another without any previous form fit.

An adverse heating of the components involved during the assemblyprocess or contamination, such as may have occurred relativelyfrequently in a conventional method may be reliably prevented by themethod according to an example embodiment of the present invention.Furthermore, there is no need to use further additional connectionelements, such as, for example, pins, clips, etc.

A secondary effect of the fastening of the torque measurement device tothe input shaft or the output shaft which may be performed reliably interms of the process may be that, if appropriate, even repeatedconnection, particularly with regard to hardened shafts, and thereforereuse are possible.

The torque measurement device may be connected, free of play, to theinput shaft or output shaft, so that it is possible, for example by anelectric motor, to assist the predetermined steering requirement exactlyand in a simple manner.

Furthermore, according to an example embodiment of the presentinvention, there may be provision for the torque measurement device tohave a magnetic ring and a sensor which are integrally formed into theinput shaft or the output shaft by the deformation elements.

By the torque measurement device being arranged with a magnetic ring,which may be fastened to an input shaft, and with a sensor for fasteningto an output shaft, the relative torque between the input shaft and theoutput shaft may be picked up in a simple manner. The torque and, fromthis, the necessary assisting force provided by the electric motor maybe determined with the aid of other parameters from the angular rotationwhich is ascertained.

The input shaft and/or the output shaft may be provided with receptionpoints for receiving the material of the torque measurement device whichis to be integrally formed locally, and the reception points may bearranged as depressions, countersinks, bores, etc.

By the reception points in the input shaft and/or the output shaft, thetorque measurement device or the magnetic ring and/or the sensor may befastened to the input shaft or to the output shaft in a simple manner.This may result in a form-fitting connection which arises from aform-fitting and frictional assembly operation. In this case, it may besufficient if one of the two parts to be connected, in this case theinput shaft and/or the output shaft, has, before the assembly operation,the possibility of the subsequent form fit.

Fastening the torque measurement device according to the method can becarried out with particularly little effort, exactly, quickly andpermanently by the reception points. Flexibility in the mounting orsetting of the torque measurement device is not influenced in the leastin this case, since the torque measurement device is designed without aprevious form fit and can therefore be oriented or attached in anydesired manner. Only after an appropriate actuation of the deformationelements, which integrally forms the material of the torque measurementdevice locally into the reception points, is there the desired permanentand reliable connection between the torque measurement device and theinput or output shaft.

The force of the deformation elements which is to be applied forconnection is reduced substantially by the reception points, with theresult that it is possible to adhere to the intended positionparticularly accurately.

In an example embodiment of the present invention, there may beprovision for the torque measurement device to be integrally formed by adeep-drawing process.

An embodiment of this type has proved to be particularly reliable interms of the process and to be simple to carry out.

For integral forming, three deformation elements arranged as deformationrams are provided, and the number and position of the reception pointsand of the deformation rams may be adapted to one another.

By the deformation elements being arranged with three deformation ramsand by correspondingly adapted reception points, a secure and reliablefastening of the torque measurement device may be possible, which,furthermore, may be carried out quickly and cost-effectively. For thispurpose, the reception points may be introduced into the shaft so as tobe offset in each case at 120°.

In an example structural embodiment of the connection, there may beprovision for the integral forming of the torque measurement device tobe checked by force/path monitoring.

By force monitoring, a connection which may be particularly reliable interms of the process is possible, since, for example, metal sheets whichare too thin or material defects are detected due to the lowerresistance. Furthermore, the path monitoring ensures that, even whenincreased resistance occurs, the metal sheet is introduced into thereception points in the intended way or, if the intended path distanceis not reached, the part is not freed.

An input shaft and/or output shaft for carrying out the method isdescribed below.

Further refinements and developments of the present invention may begathered exemplary embodiment illustrated below, in principle, withreference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view through a torque measurement devicewhich is integrally formed into an input shaft and an output shaft of asteering system.

FIG. 2 is a view in the direction of the arrow II illustrated in FIG. 1

FIG. 3 is an enlarged illustration of a magnetic ring which is arrangedon a sheet-metal ring and which is caulked with the input shaft.

DETAILED DESCRIPTION

FIG. 1 shows part of a steering system 1, in particular of arack-and-pinion power-assisted steering system, with essentially aninput shaft 2, an output shaft 3 and a torque measurement device 4.

The input shaft 2 is in this case connected, via a steering spindleconnection to a steering handle for transmitting a steering requirement.The output shaft 3 forms a drive pinion which is in engagement with arack in the usual manner. The rack may be connected in a conventionalmanner to steerable wheels via a steering linkage.

As is evident from FIG. 1, the torque measurement device 4 is fastenedor installed both on the input shaft 2 and on the output shaft 3. Thetorque measurement device 4 can thus detect a relative torque betweenthe input shaft 2 and the output shaft 3 or between the steering spindleconnection and the drive pinion. By means of the relative torque whichis detected, an electric motor is controlled via an electronic module.

As illustrated in FIG. 1, the torque measurement device 4 has a magneticring 5 and a sensor 6. In the exemplary embodiment illustrated, themagnetic ring 5 is arranged on a cylindrical sheet-metal ring 7 which,according to the method, is integrally formed locally into the inputshaft 2 by deformation elements 8 indicated merely in principle (seeFIG. 3). In a similar way to this, the sensor 6 is arranged on a holdingplate 9 by means of spiral springs 10 and is integrally formed into theoutput shaft 3 by means of the deformation elements 8.

An arrangement of the magnetic ring 5 on the input shaft 2 and of thesensor 6 on the output shaft 3 may be provided for measuring the angleof rotation between the input shaft 2 and the output shaft 3. In analternative example embodiment there may also be provision for thearrangement of the magnetic ring 5 and of the sensor 6 to be reversed.

As may be customary in hydraulic steering systems, the input shaft 2 andthe output shaft 3 are connected to a torsion bar 11. The torque canthus be calculated via the torsion bar rigidity and the measured angleof rotation.

An arrangement of the sensor 6 with the holding plate 9 in relation tothe magnetic ring 5 with the cylindrical sheet-metal ring 7 isillustrated in FIG. 2.

For integral forming of the holding plate 9 into the output shaft 3 orfor the local integral forming of the cylindrical sheet-metal ring 7into the input shaft 2, reception points 12 may be provided in theoutput shaft 3 (FIG. 1) and in the input shaft 2 (FIG. 3). The receptionpoints may be arranged as depressions, countersinks, bores 12, etc. andmay receive the material of the torque measurement device 4 which is tobe integrally formed locally. An inadvertent displacement or judderingof the torque measurement device 4 set or oriented exactly beforedeformation may thus be largely reduced.

A integral forming of the cylindrical sheet-metal ring 7 or the holdingplate 9 into the input shaft 2 or the output shaft 3 is possible, usingthree deformation elements which are arranged correspondingly uniformlyaround the input shaft 2 or the output shaft 3. A design of thedeformation elements as deformation rams 8 may be provided. The numberand position of the bores 12 may in this case be adapted in a simplemanner to the deformation rams 8. The input shaft 2 and the output shaft3 which are illustrated in the exemplary embodiment consequently in eachcase have three bores 12 which are arranged in each case so as to beoffset at 120°.

The bores 12 are designed as cylindrical bores with countersinks. A borediameter of 1 to 4 mm, e.g., 2 to 3 mm, a bore depth of 1 to 3 mm, e.g.,1.5 to 2 mm, a countersink at 45° and a countersink depth of, e.g., 0.5to 1 mm may be suitable in tests with regard to rapid, cost-effective,accurate and permanent integral forming. The edge between thecountersink and the cylindrical part of the bore 12 is responsible forfreedom from play. A large part of the holding forces is transmitted viathis edge. A 10% clearance in the bore depth may be provided forensuring the material flow.

As regards the bore 12, care must be taken to ensure that the bore onsetis not sharp-edged. The countersink may makes it possible that thematerial of the cylindrical sheet-metal ring 7 or the holding plate 9,said material being deep-drawn into the bore 12, is not sheared off. Thelocal integral forming of the material of the cylindrical sheet-metalring 7 or of the holding plate 9 according to the method may be checkedby force/path monitoring. A deep-drawing process may be suitable forintegral forming.

FIG. 3 shows fastening of the magnetic ring 5 to the input shaft 2 andof the sensor 6 to the output shaft 3 which has been carried out by anexample embodiment of the method according to the present invention.

That part of a steering system 1 which is illustrated in FIG. 1 and FIG.2 conventionally has, in addition to the components already described, aworm 13, a bearing 14 and a connecting pin 15 which connects the torsionbar 11 to the input shaft 2.

The functioning of the worm 13 and of the bearing 14 are sufficientlyconventional.

The use of a spiral spring 10 is generally conventional, in principle.The spiral spring 10 may be provided with the ribs 10 a, illustrated inFIG. 2, for protection against rotation.

In principle, it is not necessary to use a spiral spring 10 for signaltransmission, and other methods and/or arrangements, for examplecontactless transmission methods and/or arrangements, may also be usedfor this purpose.

There are various measurement principles by which an angle of rotationbetween a magnetic ring 5 and a sensor 6 may be determined or detected.

An example embodiment of the method provides, in a first method step,for aligning the deformation rams 8 and the bores 12 with one another.This may ensure that the deformation rams 8 and the bores 12 arecorrectly aligned with one another. Subsequent mutual alignment, e.g.,when the torque measurement device 4 is already positioned, may thus beavoided and, consequently, an unintentional displacement of the torquemeasurement device 4 is prevented.

The deformation rams 8 therefore advance first, without the torquemeasurement device 4 being arranged, in the direction of the input shaft2 or the output shaft 3, are aligned with the bores 12 and subsequentlymove back again.

In a second method step, the holding plate 9 having the sensor 6 isapplied to the output shaft 3 and is integrally formed locally into thebores 12 of the output shaft 3 by the deformation rams 8. Since theholding plate 9 is a round part without a previous form fit, it can beapplied to the output shaft 3 in a simple manner. A positioning exact toa hundred percent is not absolutely necessary in this case.

The sensor 6 may also be applied to the input shaft 2 in the mannerdescribed. In a further alternative example embodiment, in which thefollowing method steps may have to be adapted correspondingly, there mayalso be provision first for fastening the magnetic ring 5 with itscylindrical sheet-metal ring 7 to the input shaft 2 or the output shaft3 and subsequently for positioning and fastening the sensor 6 in thesensor 6 in relation to the magnetic ring 5.

In a third method step, the deformation rams 8 are then applied to thenot yet occupied or still free reception points. This takes place, inprinciple, in a similar manner to the first method step alreadydescribed. For this purpose, depending on the arrangement, either thesame deformation rams 8 or another unit of deformation rams 8 may beused.

In a fourth method step, after the fastening of the sensor 6, thecylindrical sheet-metal ring 7 together with the magnetic ring 5 isapplied to the input shaft 2 and is set or positioned in relation to thesensor 6 fixed in the second method step.

In a fifth method step, the cylindrical sheet-metal ring 7 together withthe magnetic ring 5, positioned in the fourth method step, is integrallyformed into the bores 12 of the input shaft 2 by means of thedeformation rams 8. After the integral forming process, the deformationrams 8 can be drawn back again.

The fastening according to the method gives rise to a permanentconnection of the torque measurement device 4 to the input shaft 2 orthe output shaft 3, said connection being reliable in terms of theprocess. The method according to an example embodiment of the presentinvention may be used for materials currently available in this sector,e.g., for sheet steel, sheet brass, VA sheet, etc. The use of sheetbrass or VA sheet as materials may provide corrosion resistance.

By means of the method described, magnets can also be fastened to aworm. The magnet then serves, here, for detecting the rotational speedof a motor and does not have to be set.

1. A method for fastening a torque measurement device for detecting arelative torque between an input shaft and an output shaft of a steeringsystem, comprising: integrally forming the torque measurement devicelocally into at lease one of the input shaft and the output shaft bydeformation elements.
 2. The method as claimed in claim 1, wherein thesteering system includes a rack-and-pinion power-assisted steeringsystem.
 3. The method according to claim 1, wherein the torquemeasurement device includes a magnetic ring and a sensor, the methodfurther comprising integrally forming the magnetic ring and the sensorinto one of the input shaft and the output shaft by the deformationelements.
 4. The method according to claim 3, further comprising:arranging the magnetic ring on a cylindrical sheet-metal ring; andintegrally forming the cylindrical sheet-metal ring into the input shaftby the deformation elements.
 5. A method for fastening a torquemeasurement device for detecting a relative torque between an inputshaft and an output shaft of a steering system, comprising: integrallyforming the torque measurement device locally into at least one of theinput shaft and the output shaft by deformation elements, the torquemeasurement device including a magnetic ring and sensor; integrallyforming the magnetic ring and the sensor into one of the input shaft andthe output shaft by the deformation elements; arranging the sensor on aholding plate by a spiral spring; and integrally forming the holdingplate into the output shaft by the deformation elements.
 6. The methodaccording to claim 1, wherein at least one of the input shaft and theoutput shaft includes a reception point arranged to receive material ofthe torque measurement device to be integrally formed locally.
 7. Themethod according to claim 6, wherein the reception point includes atleast one of a depression, a countersink and a bore.
 8. The methodaccording to claim 6, further comprising aligning the deformationelements and the reception point.
 9. A method for fastening a torquemeasurement device for detecting a relative torque between an inputshaft and an output shaft of a steering system, comprising: integrallyforming the torque measurement device locally into at least one of theinput shaft and the output shaft by deformation elements, at least oneof the input shaft and the output shaft including a reception pointarranged to receive material of the torque measurement device to beintegrally formed locally; aligning the deformation elements and thereception point; integrally forming one of: (a) a sheet-metal ring and amagnetic ring of the torque measurement device; and (b) a holding plateand a sensor of the torque measurement device; into the reception pointof one of the input shaft and the output shaft by the deformationelements.
 10. A method for fastening a torque measurement device fordetecting a relative torque between an input shaft and an output shaftof a steering system, comprising: integrally forming the torquemeasurement device locally into at least one of the input shaft and theoutput shaft by deformation elements, at least one of the input shaftand the output shaft including a reception point arranged to receivematerial of the torque measurement device to be integrally formedlocally, the reception point including at least one of a depression, acountersink and a bore; and aligning the deformation elements with anunoccupied reception point.
 11. The method according to claim 9, furthercomprising applying to one of the input shaft and the output shaft andone of setting and positioning in relation to the one of the magneticring and the sensor integrally formed in the integral forming step: (a)the sheet-metal ring and the magnetic ring; and (b) the holding plateand the sensor.
 12. The method according to claim 11, further comprisingintegrally forming into the reception point of one of the input shaftand the output shaft by the deformation elements the one of (a) thesheet-metal ring and the magnetic ring and (b) the holding plate and thesensor applied in the applying step.
 13. The method according to claim1, wherein the torque measurement device is integrally formed in theintegrally forming step by deep-drawing.
 14. A method for fastening atorque measurement device for detecting a relative torque between aninput shaft and an output shaft of a steering system, comprising:integrally forming the torque measurement device locally into at leastone of the input shaft and the output shaft by deformation elements;wherein the deformation elements include three deformation rams.
 15. Themethod according to claim 14, wherein a number and position of receptionpoints on at least one of the input shaft and the output shaft arrangedto receive material of the torque measurement device to be integrallyformed locally correspond to a number and position of the deformationrams.
 16. A method for fastening a torque measurement device fordetecting a relative torque between an input shaft and an output shaftof a steering system, comprising: integrally forming the torquemeasurement device locally into at least one of the input shaft and theoutput shaft by deformation elements; and checking the integral formingof the torque measurement device by force/path monitoring.
 17. A device,comprising: at least one of an input shaft and an output shaft arrangedfor integral formation of a torque measurement device locally into theat least one of the input shaft and the output shaft by deformationelements, the torque measurement device configured to detect a relativetorque between the input shaft and the output shaft, the at least one ofthe input shaft and the output shaft including reception points arrangedto receive material of the torque measurement device to be integrallyformed.
 18. The device according to claim 17, wherein the receptionpoints include at least one of a countersink, a depression and a bore.19. A device comprising: at least one of an input shaft and an outputshaft arranged for integral formation of a torque measurement devicelocally into the at least one of the input shaft and the output shaft bydeformation elements, the torque measurement device configured to detecta relative torque between the input shaft and the output shaft, the atleast one of the input shaft and the output shaft including receptionpoints arranged to receive material of the torque measurement device tobe integrally formed; wherein the reception points include threecylindrical bores offset at 120° and countersinks.
 20. A devicecomprising: at least one of an input shaft and an output shaft arrangedfor integral formation of a torque measurement device locally into theat least one of the input shaft and the output shaft by deformationelements, the torque measurement device configured to detect a relativetorque between the input shaft and the output shaft, the at least one ofthe input shaft and the output shaft including reception points arrangedto receive material of the torque measurement device to be integrallyformed; wherein the reception points include a bore diameter of 1 to 4mm, a bore depth of 1 to 3 mm, and a countersink at 45°.
 21. The deviceaccording to claim 20, wherein the bore diameter is 2 to 3 mm.
 22. Thedevice according to claim 20, wherein the bore depth is 1.5 to 2 mm. 23.The device according to claim 20, wherein a countersink depth is 0.5 to1 mm.
 24. The method according to claim 1, wherein the forming stepincludes deformation of the deformation elements.